The invention relates to sampling a liquified gas for analytical purposes, and more particularly, to continuously taking a sample of a liquified gas, vaporizing the gas, and transferring the vaporized gas to a remote analyzer.
Natural gas is a combustible gas that occurs in porous rock of the earth's crust and is found with or near accumulations of crude oil. Natural gas is a mixture of hydrocarbon fuels, with methane (CH.sub.4) the most common constituent, typically about 85 percent and often 90 percent or more. Ethane (C.sub.2 H.sub.6) may be present in amounts typically from 2 to 10 percent, followed by propane (C.sub.3 H.sub.8) typically 1-4 percent. Other constituents may also be present in trace amounts. The composition varies depending primarily on the original source and the storage history. The main use of natural gas is for fuel.
Since 600 cubic feet of natural gas condenses to less than 1 cubic foot of liquid, liquified natural gas (LNG) is a useful product of natural gas, particularly for storage purposes. However, because liquified natural gas has a low critical temperature, about -100.degree. F., is difficult to liquify and maintain in the liquid state. The temperature of LNG is typically about -367.degree. F. A variety of large insulated tanks have been designed for storage as well as special insulated tankers for ocean transport. The storage and transport of liquified natural gas create a possiblity of serious accidents.
The Lawrence Livermore National Laboratory has been conducting a series of tests at the Naval Weapons Center, China Lake, Calif. In these tests quantities of liquified natural gas from 5 to 40 cubic meters are spilled onto water which is much warmer than the cold LNG. The dispersion of the LNG vapor cloud in the atmosphere under various conditions and the combustion of the gas cloud are measured. In addition, the phenomenon of large and unexpected explosions known as rapid phase transformations (RPT) are being studied. The composition of the LNG varied from 94% CH.sub.4, 5% C.sub.2 H.sub.6, 1% C.sub.3 H.sub.8, having the greatest percentage of methane, to 83% CH.sub.4, 14% C.sub.2 H.sub.6, 3% C.sub.3 H.sub.8 having the highest percentage of non-methane constituents.
Because the composition of the LNG varies during the spill, it is desirable to obtain a continuous composition profile of the spill in order to study the dispersion, combustion and RPT explosions. The composition of the vapors can be measured by an IR gas detector; however, the detector cannot be placed near the spill point because it will be damaged or destroyed during the ensuing tests. Also, the LNG must be vaporized before entering the IR gas detector.
U.S. Pat. No. 3,938,391 to Winkler discloses a sampling device for liquified gases which includes a container for receiving a sample of the liquid and a communicating chamber in which the liquid is converted to a gas which is withdrawn through a valve for analysis.
U.S. Pat. Nos. 4,250,142 to Kollmai, 4,073,619 to Lawson, 4,262,522 to Reich and 4,138,891 to Graves, et al. relate generally to the detection or sampling of gases from sources including oil and gas wells and steel making vessels.
Accordingly, it is an object of the invention to provide continous sampling of liquified natural gas effluent from a spill pipe.
It is another object of the invention to continuously measure the composition of liquified natural gas flowing from a spill pipe.
It is a further object of the invention to continuously remove a sample of liquified natural gas, vaporize the liquified gas and transfer the vaporized gas to a remote IR detector.
It is also an object of the invention to provide real time LNG composition monitoring.